There is known a hybrid drive system for an automotive vehicle, wherein a power transmitting mechanism connected to drive wheels is connected to an engine and an electric motor or a motor/generator. JP-A-11-350995 discloses an example of such a hybrid drive system, which uses a variable-cylinder engine which is selectively operable in one of a full-cylinder operating state and a partial-cylinder operating state (reduced-cylinder operating state). All of the cylinders of the engine are operated in the full-cylinder operating state, and some of the cylinders are operated in the partial-cylinder operating state. The present hybrid drive system is further arranged such that a kinetic energy of the vehicle during deceleration thereof is converted by regenerative braking operation of the electric motor into an electric energy, which is stored for use by the electric motor to provide an assisting drive torque upon starting of the vehicle, for instance, to thereby improve the fuel economy of the vehicle.
However, a need to improve the fuel economy of the vehicle is unlimited, and there has been a demand for a further improvement in the fuel economy of such a vehicle using a variable-cylinder engine and an electric motor as drive power sources, as described above.
The present invention was made in view of the background situation described above. It is therefore an object of this invention to provide a control apparatus for a variable-cylinder engine or an automotive vehicle control apparatus, which apparatus permits a further improvement in the fuel economy of the vehicle.